According to digital broadcast, a plurality of broadcast services can be transmitted through a specific frequency, unlike analog broadcast. In addition, detailed information for reception of a broadcast service can be changed according to things such as broadcasters. Thus, in order to receive each broadcast service, a broadcast receiving apparatus needs to perform broadcast service scan for acquisition of connection information required to receive each broadcast service. To this end, the broadcast receiving apparatus needs to sequentially tune frequencies within a baseband as a frequency band for transmission of a broadcast service, to receive a broadcast signal, and to acquire service connection information from the received broadcast signal. Thus, a user needs to wait for completion of the broadcast service scan in order to watch broadcast. Accordingly, there has been a need to determine maximum time required to complete the broadcast service scan by many broadcasters and to complete the broadcast service scan by a broadcast receiving apparatus within the maximum time by a manufacturer of the broadcast receiving apparatus.
In general, IP/UDP/RTP header fields can be classified into static, delta, dynamic, and inferred attributes. The static is a field having a predetermined value in one end to end packet stream, corresponds to an IP address and a port number, and also corresponds to a field having well known values like in a version field of RTP or IP. The delta is a field having a predetermined difference value from a previous packet and corresponds to a sequence number, etc. The dynamic is a field that is randomly changed and corresponds to checksum, an ID of an IP packet, etc. The inferred corresponds to a field that can be inferred via another header field, etc. like the length field. Concept of context identifier (CID) has been introduced as a general header compression scheme. When a transmitter side (compressor) initially transmits a packet having a full header in a non-compression state, to which a specific CID is added, and then transmits a next packet with the same CID, from which header fields having static, delta, or inferred attribute are omitted, a receiver side (decompressor) restores an overall RTP header by adding fields omitted from a compression header received after a second packet with reference to header field information that is initially stored based on the CID. In the case of delta header, when the compressor and the decompressor store most fields of the full header and then the compressor transmits only a difference value from a previous packet, the decompressor restores the delta header by compensating a pre-stored value for the difference value.
A robust header compression (RoHC) scheme classifieds a header field into static, dynamic, and inferable, defines a compression release state at a compressor as initialization and refresh (IR), first order (FO), and second order (SO), and defines a compression release state at a decompressor as no context (NC), static context (SC), and full context (FC). The RoHC scheme initially begins to perform transmission with a low compression ratio and maintains a state in which the current compression ratio reaches a highest compression ratio as possible. In this regard, when the decompressor fails in context initialization or compression release, the compressor state is returned to IR as a lowest compression step and in this state, the compressor transmits a full header. Then, in the FO step, the compressor omits a static field and does not lastly transmit all fields that can be compressed in an SO step. State transition of the decompressor can be moved to SC and FC steps from NC as a lowest step, and an optimal compression release operation is performed in the FC step.
Robust header compression (RoHC) can be configured for a bidirectional transmission system. In the bidirectional transmission system, a RoHC compressor and a RoHC decompressor can perform an initial set up procedure and in this procedure, can transmit and receive a parameter required for the initial procedure. The procedure for transmitting and receiving the parameter required for aforementioned initial procedure can be referred as a negotiation procedure or an initialization procedure. However, a unidirectional system such as a broadcast system cannot perform the afore-mentioned negotiation procedure and needs to replace the aforementioned initialization procedure with a separate method.